1. Field of the Invention
The present invention relates to a rotatable supporting structure and more particularly to a ceramic supporting structure having portions adapted to engage dental bridgework made of porcelain which must be baked or fired during the production thereof. The supporting structure facilitates rotation of the workpiece without the necessity of removing or displacing it from its position within the furnace or oven utilized for curing the workpiece.
2. Description of the Prior Art
There are various types of supporting means which have been used in the past to support porcelain dental bridges or the like during the production thereof, while the porcelain is in its raw or pastelike state. The prior art support means are adpated with appendages which are adapted to engage the base metal supporting structure of the dental bridge and hold same keeping the porcelain in its paste form from engaging surfaces of the oven or the supporting means. Such prior art supporting structures are designed and adapted to hold the workpiece in one position only and it was necessary to move the entire supporting structure to move or rotate the workpiece in any manner. During the firing or curing of porcelain, in connection with the production of dental bridges, it is necessary to view or visually scrutinize the porcelain to determine the proper time for its removal from the oven or furnace.
It must be noted that during the heating of procelain in connection with the manufacture of bridgework, as each unit or workpiece is unique being made each individually, it is impossible to predetermine the exact amount of time which the procelain should be subjected to heat within a porcelain furnace or oven. The only way to accurately ascertain whether the proper amount of heat has been absorbed by the porcelain is by viewing the porcelain itself, which serves as a visual hardening indicator. When the porcelain is in its paste or soft state it is somewhat colorless, whereas as it absorbs heat it gains a whiteish tint. It is important during the curing of the porcelain that all portions thereof be heated to the proper degree during this initial curing, which is generally referred to in the art as the bisque bake. If parts of the porcelain have a modeled appearance it is an indication that it has not been cured to the proper degree. Generally, porcelain is applied to a base metal structure of the dental bridgework in varying depths, shapes and configurations. Therefore, portions of the procelain may be "cured" whereas other portions are not, a condition which must be avoided in order to produce a suitable product.
As is well known in the porcelain art, overbaking or curing subjects the porcelain to conditions which are undesirable structurally, and accordingly prompt removal of the porcelain at the point in time when all exposed surfaces visually indicate that the proper hardening has occurred, is required. In the past, as prior art supporting means held the bridgework in a stationary position, it was necessary to interrupt the curing or heating process by opening the furnace door, and completely removing the supporting structure with the workpiece disposed thereon, to the oven door or other open surface. To accomplish such a removal, suitable prongs or tweezers are required to hold the supporting means or move it into various positions so that one could look at all sides or 360.degree. of the workpiece. The removal of the workpiece from the oven, in order to properly view all angles of the bridgework, presented severe disadvantages as the heat loss associated with removing the workpiece from the oven is generally in the area of 400.degree.-600.degree. F. Such a severe reduction in temperature causes the porcelain to acquire glass build-up due to the silicon present in most porcelain materials. In the past, heating and reheating was required in order to allow for the inspection of the workpiece, and normally it was necessary to reheat two or three times in order to find the correct amount of curing. Accordingly, cracking of the porcelain, due to glass build-up was common which necessitated the discarding of the workpiece. As is appreciated in the art, glass build-up due to reheating greatly increases the likelihood of a defective finished product and greatly increases the cost of production.
It is, of course, possible to merely open the door of the heating oven or furnace in order to view the workpiece without moving it, which results in a heat loss of only 50.degree.-70.degree. F., but it is then impossible to view all sides of the porcelain. If the workpiece is removed too early, it is then necessary to re-introduce the workpiece as described above, which shocks the porcelain introducing glass build-up, which severely weakens the structure as well as causing surface deformities and large structural cracks. If the workpiece is left to remain in the oven too long, glass build-up is also promoted.
Also required for the preparation of porcelain bridgework is a glaze bake coating which is applied to the porcelain or a subsequent glaze bake. After the second coating or glaze bake the workpiece must then be fired at a temperature most often times higher than that at which it was cured and again, the glaze bake must be visually viewed in order to determine the proper point at which to remove the workpiece. Generally, during the two firing procedures discussed, it is common to remove the workpiece from ten or fifteen times in order to determine the proper time at which the various curing or firing steps have been completed.
During the bisque bake as well as the glaze bake it should be noted that a temperature drop in the area of 50.degree.-70.degree. F., which occurs when the oven door is opened only, does not affect the porcelain or the glaze coating and accordingly the oven door may be opened an unlimited number of times without causing any damage to the workpiece. However, heat loss in the area of 400.degree.-600.degree. F. which occurs when the workpiece is moved out of the oven for inspection does cause severe problems and structural and physical damage to the workpiece, and in some instances damage beyond the point where the product can be used.